Variable back-up ring and a sealing structure having the same

ABSTRACT

A variable back-up ring includes: a first half shell; a second half shell having a symmetrical shape to the first half shell; and an inner cavity defined by the first half shell and the second half shell. The first half shell and the second half shell are deformable depending on a magnitude of a fluid pressure acting on the first half shell and the second half shell.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority toKorean Patent Application No. 10-2020-0165648, filed on Dec. 1, 2020, inthe Korean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to a variable back-up ring, and moreparticularly, to a variable back-up ring which is deformable in a radialdirection depending on a fluid pressure, i.e., the amount (magnitude) offorce acting on an O-ring and/or a back-up ring, and a sealing structurehaving the same.

BACKGROUND

A fuel cell is an electrochemical cell that converts the chemical energyof a fuel (hydrogen) and an oxidizing agent (oxygen) into electricalenergy through redox reactions.

As the perception of environmental crisis and depletion of oil resourceshas increased, research and development of eco-friendly vehicles such aselectric vehicles (EVs) and fuel cell electric vehicles (FCEVs) haveactively been conducted.

A fuel cell system is made up of: a fuel cell stack generatingelectrical energy; a fuel supply system supplying a fuel (hydrogen) tothe fuel cell stack; an air supply system supplying oxygen of the air asan oxidizing agent required for electrochemical reaction to the fuelcell stack; and a thermal management system (TMS) removing heat ofreaction from the fuel cell stack out of the system and controlling theoperating temperature of the fuel cell stack. The fuel cell systemgenerates electricity through the electrochemical reaction between thefuel (hydrogen) and oxygen in the air and removes heat and water asreaction by-products.

The hydrogen supply system is configured to supply hydrogen, which is arelatively high-pressure fluid, to the fuel cell stack. In the hydrogensupply system, a sealing structure including an O-ring and a back-upring for holding the O-ring may be provided between two connector bodies(e.g., a valve housing and a valve fitting) that match each other,thereby preventing leakage of the high-pressure fluid. The O-ring maycreate a seal between the two connector bodies, and the back-up ring mayminimize a clearance gap between the two connector bodies to prevent theO-ring from entering the clearance gap between the two connector bodies.

When high-pressure hydrogen of 700 bar flows in such a high-pressurefluid system (the hydrogen supply system), a permeation leakage mayoccur as small-sized hydrogen molecules penetrate into a rubber(polymer) material of the O-ring, A leakage may also occur as cracks aregenerated in the O-ring due to pressurization/decompression.Specifically, as the hydrogen molecules penetrate into the rubber(polymer) material of the O-ring in the high-pressure hydrogenenvironment, O-ring swelling may occur. Accordingly, as the O-ring getscaught within the clearance gap, external cracks (extrusion) of theO-ring may occur. In addition, when the volume of hydrogen expands ashydrogen evaporates due to rapid decompression after the swelling of theO-ring, internal cracks (blister) of the O-ring may occur.

The clearance gap between the two connector bodies may be created due tomanufacturing tolerances, assembly tolerances, and the like. In order toprevent damage to the sealing structure in the high-pressure fluidsystem, the back-up ring may minimize the clearance gap between the twoconnector bodies to thereby prevent damage to the O-ring.

However, as the back-up ring is mainly made of a rigid material such asa synthetic resin material, it is difficult for the back-up ring tominimize the clearance gap between the two connector bodies.

The above information described in this background section is providedto assist in understanding the background of the inventive concept. Thebackground section may include any technical concept which is notconsidered as the prior art that is already known to those havingordinary skill in the art.

SUMMARY

The present disclosure has been made to solve the above-mentionedproblems occurring in the prior art while advantages achieved by theprior art are maintained intact.

An aspect of the present disclosure provides a variable back-up ringhaving a shape that is variable or deformable in a radial direction andprovides a sealing structure having the same.

According to an aspect of the present disclosure, a variable back-upring may include: a first half shell; a second half shell having asymmetrical shape to the first half shell; and an inner cavity definedby the first half shell and the second half shell. The first half shelland the second half shell may be deformable depending on a magnitude ofa fluid pressure acting on the first half shell and the second halfshell.

The first half shell and the second half shell may have a referenceshape when the fluid pressure is lower than a reference pressure. and

The first half shell and the second half shell may have an expandedshape when the fluid pressure is higher than a reference pressure.

The shape of the first half shell and the second half shell may varybetween the reference shape and the expanded shape as the magnitude ofthe fluid pressure varies. The reference shape may be a shape in whichthe first half shell and the second half shell contract radially inward.The expanded shape may be a shape in which the first half shell and thesecond half shell expand radially outward.

According to another aspect of the present disclosure, a sealingstructure may include: a first connector body having a groove; a secondconnector body encompassing the first connector body; an O-ringpartially received in the groove of the first connector body; and avariable back-up ring partially received in the groove of the firstconnector body, holding the O-ring. The variable back-up ring may bedeformable in a radial direction depending on a magnitude of a fluidpressure applied between the first connector body and the secondconnector body.

The variable back-up ring may include an inner circumferential surfacecontacting the groove of the first connector body and an outercircumferential surface facing an inner circumference of the secondconnector body. A position of the outer circumferential surface of thevariable back-up ring may be variable or deformable in the radialdirection of the variable back-up ring depending on the magnitude of thefluid pressure.

The shape of the variable back-up ring may be variable or deformable sothat the outer circumferential surface of the variable back-up ring maybe brought into contact with the inner circumference of the secondconnector body when the magnitude of the fluid pressure is higher than areference pressure.

The groove of the first connector body may include a base surfacerecessed radially inward from an outer circumference of the firstconnector body, a first side relatively close to a source of the fluidpressure, and a second side opposing the first side. The O-ring may berelatively close to the first side, and the variable back-up ring may berelatively close to the second side.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentdisclosure should be more apparent from the following detaileddescription taken in conjunction with the accompanying drawings:

FIG. 1 illustrates a cross-sectional view of a sealing structureaccording to an embodiment of the present disclosure;

FIG. 2 illustrates an enlarged view of portion A of FIG. 1, a state ofthe sealing structure before a back-up ring is contracted under a lowfluid pressure condition;

FIG. 3 illustrates an enlarged view of portion A of FIG. 1, a state ofthe sealing structure in which a back-up ring is expanded under a highfluid pressure condition;

FIG. 4 illustrates a cross-sectional view of a variable back-up ringaccording to an embodiment of the present disclosure;

FIG. 5 illustrates an exploded perspective view of a variable back-upring according to an embodiment of the present disclosure;

FIG. 6 illustrates a cross-sectional view of a variable back-up ringaccording to another embodiment of the present disclosure; and

FIG. 7 illustrates a perspective view of the variable back-up ringillustrated in FIG. 6.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure are described indetail with reference to the accompanying drawings. In the drawings, thesame reference numerals are used throughout to designate the same orequivalent elements. In addition, a detailed description of well-knowntechniques associated with the present disclosure has been omitted inorder not to unnecessarily obscure the gist of the present disclosure.

Terms such as first, second, A, B, (a), and (b) may be used to describethe elements in the embodiments of the present disclosure. These termsare only used to distinguish one element from another element, and theintrinsic features, sequence or order, and the like of the correspondingelements are not limited by the terms. Unless otherwise defined, allterms used herein, including technical or scientific terms, have thesame meanings as those generally understood by those having ordinaryskill in the field of art to which the present disclosure belongs. Suchterms as those defined in a generally used dictionary are to beinterpreted as having meanings consistent with the contextual meaningsin the relevant field of art. Such terms are not to be interpreted ashaving ideal or excessively formal meanings unless clearly defined ashaving such in the present application.

The present disclosure relates to a sealing structure for preventingleakage of a high-pressure fluid from a high-pressure fluid system suchas a hydrogen supply system of a fuel cell and relates to a back-up ringholding an O-ring in the sealing structure. In particular, according toembodiments of the present disclosure, an outer diameter of the back-upring may be variable or deformable in a radial direction depending onthe magnitude of a force or fluid pressure acting on the O-ring and theback-up ring.

Referring to FIGS. 1 and 2, a sealing structure 8 according to anembodiment of the present disclosure may include a first connector body1, a second connector body 2 encompassing the first connector body 1, anO-ring 5 received in a groove 12 of the first connector body 1, and aback-up ring 6 holding the O-ring 5.

The first connector body 1 may have an outer circumference 11. Theannular groove 12 may be defined in the outer circumference 11 and thefirst connector body 1 may have a cylindrical shape. The groove 12 mayhave a base surface 15 recessed radially inward from the outercircumference 11 of the first connector body 1, a first side 13relatively close to a source of a fluid pressure, and a second side 14opposing the first side 13. The base surface 15 may be located betweenthe first side 13 and the second side 14. The groove 12 may have apredetermined depth d. The depth d of the groove 12 may be a distancebetween the base surface 15 and the outer circumference 11.

The second connector body 2 may have an inner circumference 21 tightlyencompassing the outer circumference 11 of the first connector body 1and the second connector body 2 may have a cylindrical shape. The outercircumference 11 of the first connector body 1 and the innercircumference 21 of the second connector body 2 may face each other. theinner circumference 21 of the second connector body 2 may be spacedapart from the outer circumference 11 of the first connector body 1 by aclearance gap cg. In other words, the clearance gap cg may be definedbetween the outer circumference 11 of the first connector body 1 and theinner circumference 21 of the second connector body 2.

For example, the first connector body 1 may be a valve fitting of ahigh-pressure hydrogen valve having a cylindrical shape. The secondconnector body 2 may be a valve body of the high-pressure hydrogen valvehaving an opening into which the valve fitting is tightly fitted.

Alternatively, the first connector body 1 and the second connector body2 may be part of a pressure regulator, a shut-off valve, a check valve,a flow valve, or a pipe fitting.

The O-ring 5 may be an annular seal at least partially received in thegroove 12 of the first connector body 1. The O-ring 5 may be relativelyclose to the first side 13 of the groove 12. The O-ring 5 may be made ofat least one material or a mixture of two or more materials amongvarious materials such as acrylonitrile butadiene rubber (NBR),hydrogenated acrylonitrile butadiene rubber (HNBR), fluorocarbon (FPM,FKM, Viton™), ethylene propylene diene monomer (EPDM), neoprenechloroprene (CR), silicone (VMQ, PVMQ), acrylate (ACM) and polyurethane(AU).

The back-up ring 6 may be an annular ring at least partially received inthe groove 12 of the first connector body 1. The back-up ring 6 may berelatively close to the second side 14 of the groove 12. Referring toFIGS. 1-3, the back-up ring 6 may be interposed between the O-ring 5 andthe second side 14 within the groove 12 of the first connector body 1and the back-up ring 6 may hold the O-ring 5. For example, the back-upring 6 may be made of an elastic material which is easily deformable,such as engineering plastic or rubber.

The outer diameter of the back-up ring 6 may be variable or deformablein the radial direction of the back-up ring 6 depending on the magnitudeof the force or fluid pressure acting on the back-up ring 6.Specifically, when the fluid pressure applied between the outercircumference 11 of the first connector body 1 and the innercircumference 21 of the second connector body 2 acts on the O-ring 5 andthe back-up ring 6, the back-up ring 6 may expand or contract in a widthdirection of the back-up ring 6 while contracting or expanding in theradial direction of the back-up ring 6 depending on the magnitude of thefluid pressure.

The back-up ring 6 may include an inner circumferential surface 9 afacing the center of the back-up ring 6 and an outer circumferentialsurface 9 b located away from the center of the back-up ring 6. Theinner circumferential surface 9 a may contact the base surface 15 in thegroove 12 of the first connector body 1 and the outer circumferentialsurface 9 b may face the second connector body 2. When the back-up ring6 contracts or expands in the radial direction of the back-up ring 6depending on the magnitude of the fluid pressure, the innercircumferential surface 9 a of the back-up ring 6 may be supported tothe base surface 15 of the groove 12. Accordingly, the position of theinner circumferential surface 9 a of the back-up ring 6 may not changeand the position of the outer circumferential surface 9 b of the back-upring 6 may be varied. Specifically, the outer circumferential surface 9b of the back-up ring 6 may be spaced apart from the inner circumference21 of the second connector body 2 (see FIG. 2) or be brought intocontact with the inner circumference 21 of the second connector body 2(see FIG. 3).

Referring to FIG. 2, when the fluid pressure is a relatively lowpressure which is lower than a reference pressure, the back-up ring 6may have a reference shape. The reference shape refers to a shape of theback-up ring 6 expanding in the width direction and contracting radiallyinward. Here, the reference pressure may be a minimum pressure allowingthe back-up ring 6 to expand radially outward. For example, thereference pressure may be 100 bar to 700 bar. Since the innercircumferential surface 9 a of the back-up ring 6 is supported to thebase surface 15 of the groove 12, the position of the innercircumferential surface 9 a of the back-up ring 6 may not change and theouter circumferential surface 9 b of the back-up ring 6 may be spacedapart from the inner circumference 21 of the second connector body 2. Asthe back-up ring 6 contracts radially inward, the outer diameter of theback-up ring 6 may be reduced to the minimum. Accordingly, the thicknessof the back-up ring 6 may be a minimum thickness h1, and the width ofthe back-up ring 6 may be expanded to a maximum width w1. Here, as thewidth of the back-up ring 6 is expanded to the maximum width w1, theback-up ring 6 may push the O-ring 5 toward the first side 13.Accordingly, a contact area between an outer circumferential surface ofthe O-ring 5 and the inner circumference 21 of the second connector body2 may increase. Thus, sealing performance achieved by the O-ring 5 maybe maximized even in a condition in which the fluid pressure is low. Thewidth, thickness, and the like of the O-ring 5 may be appropriatelyselected to adjust a compression rate/a groove filling rate depending onthe degree of shape variation (or deformation) of the back-up ring 6.

Referring to FIG. 3, when the fluid pressure is a relatively highpressure, which is higher than the reference pressure, the back-up ring6 may have an expanded shape. The expanded shape refers to a shape ofthe back-up ring 6 contracting in the width direction and expandingradially outward. Since the inner circumferential surface 9 a of theback-up ring 6 is supported to the base surface 15 of the groove 12, theposition of the inner circumferential surface 9 a of the back-up ring 6may not change and the outer circumferential surface 9 b of the back-upring 6 may tightly contact the inner circumference 21 of the secondconnector body 2. As the back-up ring 6 expands, the outer diameter ofthe back-up ring 6 may be increased to the maximum. Accordingly, thethickness of the back-up ring 6 (a distance between the innercircumferential surface 9 a and the outer circumferential surface 9 b)may be a maximum thickness h2, and the width of the back-up ring 6 maybe contracted to a minimum width w2. The maximum thickness h2 of theback-up ring 6 may be set to be greater than the sum of the depth d ofthe groove 12 and the clearance gap cg (h2>d+cg). As the outercircumferential surface 9 b of the back-up ring 6 tightly contacts theinner circumference 21 of the second connector body 2, the back-up ring6 may completely block the clearance gap cg between the first connectorbody 1 and the second connector body 2.

Referring to FIG. 4, the back-up ring 6 may include a first half shell 6a extending in an annular shape, a second half shell 6 b symmetricallyconnected to the first half shell 6 a, and an inner cavity 6 c definedby the first half shell 6 a and the second half shell 6 b.

The first half shell 6 a may face the first side 13 and the second halfshell 6 b may face the second side 14. In other words, the first halfshell 6 a and the second half shell 6 b may oppose each other. The firsthalf shell 6 a may contact the O-ring 5 and the second half shell 6 bmay contact the second side 14 of the groove 12. As the inner cavity 6 cis defined by the first half shell 6 a and the second half shell 6 b,the inner cavity 6 c may be a closed cavity.

When the force or fluid pressure acting on the first half shell 6 a andthe second half shell 6 b is lower than the reference pressure, thefirst half shell 6 a and the second half shell 6 b may have a referenceshape (see FIG. 2). When the first half shell 6 a and the second halfshell 6 b maintain the reference shape, the first half shell 6 a and thesecond half shell 6 b may be convex in an opposite direction toward theoutside of the inner cavity 6 c. The first half shell 6 a and the secondhalf shell 6 b may have a predetermined radius of curvature. The radiusof curvature of the first half shell 6 a may be the same as or bedifferent from the radius of curvature of the second half shell 6 b. Inother words, when the force or fluid pressure acting on the first halfshell 6 a and the second half shell 6 b is lower than the referencepressure, the first half shell 6 a and the second half shell 6 b mayexpand in the width direction of the back-up ring 6. Thus, the firsthalf shell 6 a and the second half shell 6 b may contract inward in theradial direction of the back-up ring 6. In short, the reference shapemay be a shape in which the first half shell 6 a and the second halfshell 6 b expand in the width direction of the back-up ring 6 whilecontracting inward in the radial direction of the back-up ring 6.

When the force or fluid pressure acting on the first half shell 6 a andthe second half shell 6 b is higher than the reference pressure, thefirst half shell 6 a and the second half shell 6 b may have an expandedshape (see FIG. 3). When the first half shell 6 a and the second halfshell 6 b maintain the expanded shape, the first half shell 6 a and thesecond half shell 6 b may be relatively flattened. Accordingly, thefirst half shell 6 a and the second half shell 6 b may contract in thewidth direction of the back-up ring 6. Thus, the first half shell 6 aand the second half shell 6 b may expand outward in the radial directionof the back-up ring 6. In short, the expanded shape may be a shape inwhich the first half shell 6 a and the second half shell 6 b contract inthe width direction of the back-up ring 6 while expanding outward in theradial direction of the back-up ring 6.

As described above, the shape of the first half shell 6 a and the secondhalf shell 6 b may vary between the reference shape and the expandedshape as the magnitude of the force or fluid pressure varies.

Referring to FIG. 2, when no fluid pressure or low fluid pressure actson the back-up ring 6, the first half shell 6 a and the second halfshell 6 b may maintain the reference shape and the inner cavity 6 c mayhave a maximum volume. Referring to FIG. 3, when high fluid pressureacts on the back-up ring 6, the first half shell 6 a and the second halfshell 6 b may expand outward in the radial direction of the back-up ring6 and the inner cavity 6 c may have a minimum volume.

The first half shell 6 a may include a first outer surface 31 facing theoutside of the back-up ring 6 and a first inner surface 32 facing theinner cavity 6 c. The first outer surface 31 may partially contact theO-ring 5 and the first inner surface 32 may define at least a portion ofthe inner cavity 6 c.

In an initial state in which no fluid pressure or low fluid pressureacts on the back-up ring 6, the first half shell 6 a may have thereference shape, which is convex toward the outside of the inner cavity6 c. Referring to FIG. 4, in the reference shape of the first half shell6 a, the first outer surface 31 may include an apex 31 a, a curvedsurface 31 b extending from the apex 31 a toward the innercircumferential surface 9 a of the back-up ring 6, and a curved surface31 c extending from the apex 31 a toward the outer circumferentialsurface 9 b of the back-up ring 6. The first inner surface 32 mayinclude an apex 32 a, a curved surface 32 b extending from the apex 32 atoward the inner circumferential surface 9 a of the back-up ring 6, anda curved surface 32 c extending from the apex 32 a toward the outercircumferential surface 9 b of the back-up ring 6.

The second half shell 6 b may include a second outer surface 33 facingthe outside of the back-up ring 6 and a second inner surface 34 facingthe inner cavity 6 c. The second outer surface 33 may partially contactthe second side 14 of the groove 12 and the second inner surface 34 maydefine at least a portion of the inner cavity 6 c.

In the initial state in which no fluid pressure or low fluid pressureacts on the back-up ring 6, the second half shell 6 b may have thereference shape, which is convex toward the outside of the back-up ring6. Referring to FIG. 4, in the reference shape of the second half shell6 b, the second outer surface 33 may include an apex 33 a, a curvedsurface 33 b extending from the apex 33 a toward the innercircumferential surface 9 a of the back-up ring 6, and a curved surface33 c extending from the apex 33 a toward the outer circumferentialsurface 9 b of the back-up ring 6. The second inner surface 34 mayinclude an apex 34 a, a curved surface 34 b extending from the apex 34 atoward the inner circumferential surface 9 a of the back-up ring 6, anda curved surface 34 c extending from the apex 34 a toward the outercircumferential surface 9 b of the back-up ring 6.

Referring to FIGS. 4 and 5, an inner circumferential edge of the firsthalf shell 6 a and an inner circumferential edge of the second halfshell 6 b may be joined through an adhesive and/or the like. An outercircumferential edge of the first half shell 6 a and an outercircumferential edge of the second half shell 6 b may be joined throughan adhesive and/or the like.

FIG. 6 illustrates a back-up ring according to another embodiment of thepresent disclosure. Referring to FIG. 6, a back-up ring 16 may includean inner circumferential surface 19 a facing the center of the back-upring 16 and an outer circumferential surface 19 b located away from thecenter of the back-up ring 16. The inner circumferential surface 19 amay contact the base surface 15 of the groove 12 of the first connectorbody 1 and the outer circumferential surface 19 b may face the secondconnector body 2. When the back-up ring 16 contracts or expands in theradial direction depending on the magnitude of a fluid pressure, theinner circumferential surface 19 a of the back-up ring 16 may besupported to the base surface 15 of the groove 12. Accordingly, theposition of the inner circumferential surface 19 a of the back-up ring16 may not change and the position of the outer circumferential surface19 b of the back-up ring 16 may be varied.

The back-up ring 16 may include a first half shell 16 a facing the firstside 13, a second half shell 16 b facing the second side 14, and aninner cavity 16 c defined by the first half shell 16 a and the secondhalf shell 16 b.

The first half shell 16 a may contact the O-ring 5 and the second halfshell 16 b may contact the second side 14 of the groove 12. As the innercavity 16 c is defined by the first half shell 16 a and the second halfshell 16 b, the inner cavity 16 c may be a closed cavity.

The first half shell 16 a may include a first outer surface 41 facingthe outside of the back-up ring 16 and a first inner surface 42 facingthe inner cavity 16 c. The first outer surface 41 may partially contactthe O-ring 5 and the first inner surface 42 may define at least aportion of the inner cavity 16 c.

In an initial state in which no fluid pressure or low fluid pressureacts on the back-up ring 16, the first half shell 16 a may have areference shape, which is convex toward the outside of the back-up ring16. Referring to FIG. 6, in the reference shape of the first half shell16 a, the first outer surface 41 may include an apex 41 a, an inclinedsurface 41 b extending obliquely from the apex 41 a toward the innercircumferential surface 19 a of the back-up ring 16, and an inclinedsurface 41 c extending obliquely from the apex 41 a toward the outercircumferential surface 19 b of the back-up ring 16. The first innersurface 42 may include an apex 42 a, an inclined surface 42 b extendingobliquely from the apex 42 a toward the inner circumferential surface 19a of the back-up ring 16, and an inclined surface 42 c extendingobliquely from the apex 42 a toward the outer circumferential surface 19b of the back-up ring 16.

The second half shell 16 b may include a second outer surface 43 facingthe outside of the back-up ring 16 and a second inner surface 44 facingthe inner cavity 16 c. The second outer surface 43 may partially contactthe second side 14 of the groove 12 and the second inner surface 44 maydefine at least a portion of the inner cavity 16 c.

In the initial state in which no fluid pressure or low fluid pressureacts on the back-up ring 16, the second half shell 16 b may have areference shape, which is convex toward the outside of the back-up ring16. Referring to FIG. 6, in the reference shape of the second half shell16 b, the second outer surface 43 may include an apex 43 a, an inclinedsurface 43 b extending obliquely from the apex 43 a toward the innercircumferential surface 19 a of the back-up ring 16, and an inclinedsurface 43 c extending obliquely from the apex 43 a toward the outercircumferential surface 19 b of the back-up ring 16. The second innersurface 44 may include an apex 44 a, an inclined surface 44 b extendingobliquely from the apex 44 a toward the inner circumferential surface 19a of the back-up ring 16, and an inclined surface 44 c extendingobliquely from the apex 44 a toward the outer circumferential surface 19b of the back-up ring 16.

As described above, as the first half shell 6 a or 16 a and the secondhalf shell 6 b or 16 b are convex in the opposite direction, the shapeof the back-up ring 6 or 16 may be easily variable in the radialdirection.

As set forth above, according to embodiments of the present disclosure,the shape of the back-up ring may be variable or deformable in theradial direction depending on the magnitude of the fluid pressure actingon the back-up ring and/or the O-ring. The variable back-up ring mayexpand radially outward in the condition in which the fluid pressure ishigher than the reference pressure, thereby completely blocking orminimizing the clearance gap between the first connector body and thesecond connector body. Thus, the sealing performance between the firstconnector body and the second connector body may be maximized.

Hereinabove, although the present disclosure has been described withreference to several embodiments and the accompanying drawings, thepresent disclosure is not limited thereto. The present disclosure andthe embodiments may be variously modified and altered by those havingordinary skill in the art to which the present disclosure pertainswithout departing from the spirit and scope of the present disclosureclaimed in the following claims.

What is claimed is:
 1. A variable back-up ring, comprising: a first halfshell; a second half shell having a symmetrical shape to the first halfshell; and an inner cavity defined by the first half shell and thesecond half shell, wherein the first half shell and the second halfshell are deformable depending on a magnitude of a fluid pressure actingon the first half shell and the second half shell.
 2. The variableback-up ring according to claim 1, wherein the first half shell and thesecond half shell have a reference shape when the fluid pressure islower than a reference pressure, and wherein the reference shape is ashape in which the first half shell and the second half shell contractradially inward.
 3. The variable back-up ring according to claim 1,wherein the first half shell and the second half shell have an expandedshape when the fluid pressure is higher than a reference pressure, andwherein the expanded shape is a shape in which the first half shell andthe second half shell expand radially outward.
 4. The variable back-upring according to claim 2, wherein the shape of the first half shell andthe second half shell varies between the reference shape and an expandedshape as the magnitude of the fluid pressure varies.
 5. A sealingstructure, comprising: a first connector body having a groove; a secondconnector body encompassing the first connector body; an O-ringpartially received in the groove of the first connector body; and avariable back-up ring partially received in the groove of the firstconnector body, holding the O-ring, the variable back-up ring beingdeformable in a radial direction depending on a magnitude of a fluidpressure applied between the first connector body and the secondconnector body.
 6. The sealing structure according to claim 5, whereinthe variable back-up ring includes an inner circumferential surfacecontacting the groove of the first connector body and an outercircumferential surface facing an inner circumference of the secondconnector body, and wherein a position of the outer circumferentialsurface of the variable back-up ring is variable in the radial directionof the variable back-up ring depending on the magnitude of the fluidpressure.
 7. The sealing structure according to claim 5, wherein theshape of the variable back-up ring is variable so that the outercircumferential surface of the variable back-up ring is brought intocontact with the inner circumference of the second connector body whenthe magnitude of the fluid pressure is higher than a reference pressure.8. The sealing structure according to claim 5, wherein the groove of thefirst connector body includes a base surface recessed radially inwardfrom an outer circumference of the first connector body, a first siderelatively close to a source of the fluid pressure, and a second sideopposing the first side, wherein the O-ring is relatively close to thefirst side, and wherein the variable back-up ring is relatively close tothe second side.